When setting a prefix for a path-like environment variable, the
deduplication code in set_env_prefix reads past the NUL byte at the end
of the env val and into the next entry. This corrupts the resultant env
value with data from the next env var, or other data sitting after it.
0fdcb958d3 (makeBinaryWrapper: If prefix/suffix already exists, remove
the original (#451031), 2025-12-11) changed the C code generated by
makeBinaryWrapper. The tests for makeBinaryWrapper check the exact code
that's generated, so they need updating.
Fixes#505339.
